Two explosions have been heard at Brussels airport with video and stills pictures showing smoke rising from one of the terminal buildings.
The incident came as the Belgian capital was on a state of high alert following the arrest of Paris terror attack suspect Salah Abdeslam in the city last week.
Sky News Middle East correspondent Alex Rossi, who was at the airport en route for Tel Aviv, told the channel: “I could feel the buildings move.”
According to reports the incident centred on an American Airlines desk in a departure hall.
Belgian media were reporting several casualties.
Mr Rossi told Sky News people were “dazed and shocked”.
He said: “The word is definitely two explosions.
“The thinking here by everybody is that it is some kind of terrorist attack although that hasn’t been verified by anyone here at the airport
“No word too of casualties. Don’t know how the explosion took place, the method if you like. But it certainly seems Brussels airport has been targeted in a terrorist attack.
“We are all being moved out of the airport now towards the emergency exit. There is a great deal of confusion here. Certainly there are a number of very upset, as you might imagine, very frightened people.”
He added: “There are fears that there might be other attackers.”
Images on social media showed shattered windows and smoke rising from an airport building.
Video footage shot from an airport car park showed dozens of people fleeing in terror.
Abdeslam, suspected as a planner in the attacks that killed 130 people in Paris, was arrested on Friday after a four-month manhunt, in the same neighbourhood in Brussels where he grew up.
But the Belgian authorities fear he had accomplices while on the run who are still at large and could pose a threat.
Belgian prosecutor Frederic Van Leeuw told reporters at a news conference in Brussels on Monday: “(It’s clear) we have a general threat.”
Mr Van Leeuw said investigators hope to find out the details of Abdeslam’s actions between the November 13 attacks and his arrest, “if he decides to tell us”.
Abdeslam, 26, a French citizen who grew up in Brussels’ Molenbeek neighbourhood, slipped through police fingers on several occasions, including the day after the attacks.
— Heber Rowan (@HeberRowan) March 22, 2016
He was interviewed three times on Saturday, the day after his capture – once by prosecutors and twice by an investigating judge – and “wasn’t in great shape“ because he had been shot in the leg by police during his capture, Mr Van Leeuw said.
Belgian prosecutors appealed to the public on Monday for information about a man who allegedly travelled to Hungary last year with the top suspect in the Paris attacks.
The federal prosecutor’s office said in a statement they are seeking details about 24-year-old Najim Laachraoui, who is said to have travelled to Syria in February 2013. It said Laachraoui was checked by guards at the Austria-Hungary border while driving in a Mercedes with Abdeslam and one other person.
Laachraoui is said to have rented a house under the name of Soufiane Kayal in the Belgian town of Auvelais that was allegedly used as a safe house. Prosecutors said traces of his DNA were found there.
Laachraoui is “someone who must explain himself,” the prosecutor said, stressing that “clues” do not amount to proof.
Abdeslam has a court hearing on Wednesday. France has requested his extradition but Abdeslam’s lawyer says his client will fight the request.
Belgian media are reporting 13 fatalities and and 35 people injured.
Mr Rossi, who had checked his luggage through the main baggage area and was at a departure gate, said he thought he was “fairly close” to the explosions but he could not be sure.
He told Sky News as he was being ushered out of the airport along with other passengers: “We felt the walls of the building rock. Dust came down from the ceiling.
“I think it was a very big explosion – hardly surprising the windows are blown out.
“I would expect if there were people around when those explosions happened – we heard two explosions – there will be a number of casualties.”
Local reports suggest the explosion happened at the check in desk of American Airlines.
Belgian interior minister says the terror level has gone up to its maximum level in wake of airport explosions.
Now reports are coming in of an explosion in a metro station.
Belgian media say an explosion has occurred at a metro station near the European Union headquarters in the Maelbeek area of Brussels. (click here for more)
All metro stations in Brussels are closing now after the explosion.
Several people are feared dead and many injured after suspected terrorist bomb attacks in Brussels.
The Belgian capital’s airport was rocked by a double blast with reports of up to 10 dead and many more injured.
Another blast was reported by local media at a Metro station in the city, close to European Union buildings.
The suspected terror attack came as Brussels was on the highest level of alert following the arrest of Paris atrocity suspect Salah Abdeslam in the city last week.
An American Airlines spokesman said: “We are aware of an incident at the Brussels airport departure hall and are taking care of our customers, employees and contractors. At this time, all of our employees and contractors are accounted for with no reported injuries.
“American Airlines flight 751 has been cancelled for today. When operations at the airport resume, we will re-accommodate our customers.”
The Belgian state broadcaster has just claimed that the attack at Zaventem airport was a suicide attack.
There have been 2 explosions at the airport. Building is being evacuated. Don't come to the airport area.
— Brussels Airport (@BrusselsAirport) March 22, 2016